1. Field of the Invention
The present invention relates to a semiconductor device that is thin and lightweight, and a manufacturing method thereof. Specifically, a semiconductor device using a substrate having a thin thickness or a film-shaped substrate, and a manufacturing method thereof.
2. Description of the Related Art
In recent years, cellular phones spread with the progress of communication technology. It is expected that cellular phones transmit moving image and more communication are expected more in future. On the other hand, laptop computers for mobile have been produced due to the weight saving. A large number of personal digital assistances referred to as PDA that begin from electronic notebook have been produced, and diffused. Moreover, most of such personal digital assistances are each mounted with a flat panel display by the development of display devices.
In such a display device, the brightness around the display device is detected, and its display luminance is adjusted. Thus, by detecting the brightness around the display device to obtain moderate display luminance, useless electric power can be reduced. For example, such an optical sensor apparatus for controlling luminance is used for cellular phones and laptop computers (for example, Patent Document 1).
As a material for an optical sensor, semiconductor is mainly used. Silicon is taken as a representative example of a semiconductor material. An optical sensor using silicon is formed by single crystal silicon or polysilicon, or amorphous silicon. An optical sensor using single crystal silicon or polysilicon has the highest sensitivity in an infrared region at around 800 nm, and has sensitivity at most around 1100 nm. Therefore, in the case that the optical sensor using single crystal silicon or polysilicon senses white fluorescent light that hardly include a spectrum of an infrared region and sunlight that has a wide spectrum from an ultraviolet region to an infrared region, there is a problem that sensing result of each light is different while actual brightness is the same.
On the other hand, an optical sensor using amorphous silicon hardly has sensitivity against light in an infrared region, and has the highest sensitivity in a range of approximately 500 to 600 nm that is central of wavelength of visible light region. In addition, the optical sensor using amorphous silicon has sensing characteristics that is like human visibility. Therefore, amorphous silicon is preferably used for the optical sensor.
A plastic substrate is thin and lightweight. Therefore, a wiring substrate that is mounted with an optical sensor formed over the plastic substrate and electronic devices using the wiring substrate can be manufactured to be thin and downsized.
Moreover, in the case of manufacturing an optical sensor using film-shaped substrate, a Roll-To-Roll method can be used. Therefore, the productivity of such optical sensor is improved.    [Patent Document 1] Japanese Patent Laid-Open No. 2003-60744 bulletin
However, a connection terminal of a wiring substrate cannot be formed on a side face of a plastic substrate because of its thin thickness. Therefore, the connection terminal is formed on one face, that the face that faces the wiring substrate. The wiring substrate and an optical sensor are fixed by only one face via a conductive material. The area of the face is small, thus, there is a problem that the mounting intensity is weaker than that of a side electrode structure.
In addition, it is difficult to see a junction between an electrode terminal of the optical sensor and an electrode pad to judge whether they connect to each other surely, because a region where the wiring substrate is connected to the optical sensor is the lower part of a substrate of the optical sensor.
Moreover, a film-shaped optical sensor is hard to mount over the wiring substrate because of its flexibility.